Fluid-cooled data centres without air coinditioning, and methods for operating same

ABSTRACT

Removal of heat generated by IT equipment in a data centre is facilitated by heat changing units mounted to back sides of open computer storage racks in which the IT equipment is mounted. One or more fans in the IT equipment generate an air flow across the IT equipment, and a heat exchanging unit mounted to the back side of the rack transfers heat in the air flow to a fluid coolant flowing through the heat exchanging unit. The heat exchanging unit has an air back pressure that does not significantly impede the air flow across the IT equipment, and a low fluid pressure drop for the fluid coolant, so that a cold air exhaust temperature of air exiting the heat exchanging unit is less than or equal to the room air temperature of input air entering the computer rack.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/398,758, filed Nov. 4, 2014 and titled“Fluid-Cooled Data Centres Without Air Conditioning, and Methods forOperating Same,” which is a national stage application (under 35 U.S.C.§ 371) of PCT/EP2013/001391, filed May 10, 2013, which claims thebenefit of European Application No. 12003748.6, filed May 11, 2012, andEuropean Application No. 12007913.2, filed Nov. 23, 2012, each of whichis incorporated herein by reference in its entirety.

DETAILED DESCRIPTION

The present invention relates to a method for operating a data centre,which is adapted to house a multiplicity/plurality of racks beingdesigned to provide storage space for IT equipment. The data centre isequipped with cooling means in order to provide dissipation of heatbeing generated by the IT equipment.

In the prior art, there exist various data building structures forhousing a multiplicity of racks, each of which comprising storage spacefor IT equipment.

Conventional data centres most typically are buildings, which comprise afalse floor for a computer infrastructure, which is typically housed in19″ rack enclosures. In conventional data centres, the cooling is stillaccomplished by cold air, which is pumped into the false floors havingholes at the appropriate locations in front of the racks. In this waycold air is supplied at the air intakes of the computer racks. Thisdesign typically requires the concept of guided airflows, feeding coldair into the racks and removing the heat from the IT equipment.

WO 2010/000440 discloses a typical state of the art conventional datacentre building in FIG. 1. This conventional design is somehowdisadvantageous, because the single racks have to be designed as closedracks and the air flow through respective racks has to be surveyed andcontrolled in order to avoid pumping unnecessary amounts of cold airfrom the cold aisle. There exist various concepts, providing aregulation of the air flow into the cold aisle, such that the fansproviding the air flow operate at the lowest possible power. The hot airgenerated by equipment inside the rack is fed back to heat exchangersbeing located somewhere else in the data centre building. The heated airis either cooled down again or fresh air is used in order to provide astream of cold air.

The prior art, such as WO 2010/000440, outlines the use of water cooledracks for high density data centres. In the prior art the heat of theelectronic equipment is transferred to cooling water by way of heatexchangers, as disclosed in WO 2010/000440, or either mounted in theracks or in the aisles. Other prior art uses direct cooling of theelectronic equipment installed in the racks with water.

Besides the typical state of the art conventional data centre building,WO 2010/000440 discloses a new energy efficient architecture formulti-storey computer data centre using liquid cooling media fordissipation of heat being generated by the IT equipment. The so calledGreen-IT concept realised by WO 2010/000440 allows the reduction ofenergy consumption for cooling. Conventional data centres often requireup to 50%, and even more, of their energy consumption for cooling. Thenovel cooling concept of WO 2010/000440 enables data centres whichrequire less than 10% (partial PUE<1.1) of their energy for cooling.

The stationary multi-storey computer data centre of WO 2010/000440becomes a kind of benchmark for later Green-IT concepts to follow as aconstant development towards energy efficient data centre.

However, stationary computer data centers as disclosed in WO 2010/000440require a constant demand for such centres and therefore are consideredas long-time investments. In addition, mobile data centres become moreand more attractive, because such mobile data centre container caneasily be installed in the near neighborhood and contain their owninfrastructure so that they can be “plugged-in” where stationarycomputer data centre are undersized and/or only temporary needs exist.

The design of the data centres, whether they are mobile or stationary issubject to constant improvement to optimise the costs for cooling the ITequipment. Beside the design, the methods for operating such data centreallow for further improvement to achieve optimised energy consumptionfor cooling.

This invention is to provide such a method for operating a stationary ormobile data centre unit.

Therefore, the instant invention relates to a method for operating adata centre comprising:

-   (i) a building for housing a multiplicity of racks (202), each rack    being an open rack housing IT equipment,-   (ii) the racks (202) being an open rack housing IT equipment (200)-   (iii) the racks (202) comprise heat exchanging means (206, 207)    being adapted to transfer the heat generated by the IT equipment to    a fluid coolant, said heat exchanging means being an element of the    racks or an element attached to the racks,-   (iv) at least one first cooling circuit (203, 204), said cooling    circuit being a closed cooling circuit, which is adapted to supply    the heat exchanging means (206, 207) of the racks (202) with a fluid    coolant and is further adapted to convey the heated coolant away    from the heat exchanging means (206, 207) of the racks (202) through    the reflux of the cooling circuit,-   (v) said first cooling circuit (203, 204) being connected to a    source providing coldness, said source being located outside the    space housing the multiplicity of racks,-   (vi) the IT equipment (200) located in the respective racks having    active means, preferably fans, for cooling parts of the IT    equipment, preferably the CPU and/or GPU and/or a storage hardware,    said active means creating an air flow (205) in the rack towards the    heat exchanging means (206, 207) being an element of the racks or an    element attached to the racks,-   (vii) said racks (202) having no other active means, in particular    fans, except for those contained within the aforementioned IT    equipment, for creating an air flow in the rack towards the heat    exchanging means being an element of the racks or an element    attached to the racks,-   (viii) said building for housing the multiplicity of racks (202)    comprising no other active means, except for those contained within    the aforementioned IT equipment (200), for creating an guided air    flow,-   (ix) at least one electrical power input,-   (x) at least one mean for distributing the electrical power from the    power input to the individual racks, allowing redundant power    supplies in every rack, comprising the measures-   (a) providing a fluid coolant from the source providing coldness to    the heat exchanging means (206, 207) of the racks (202) within the    first cooling circuit, said fluid coolant input flow entering the    heat exchanging means (206, 207) having a temperature of 1K to 5K,    preferably 1K to 3K, more preferred 1K to 2K, below the temperature    of the fluid coolant return flow exiting the heat exchanging means    (206, 207) of the racks (202),-   (b) controlling the fluid coolant flow within the first cooling    circuit (205) which is adapted to supply the heat exchanging means    (206, 207) of the racks (202) to maintain the temperature of fluid    coolant entering the heat exchanging means (206, 207) of the racks    (202) (input flow) having a temperature of 1K to 5K, preferably 1K    to 3K, more preferred 1K to 2K, below the temperature of the fluid    coolant return flow exiting the heat exchanging means (206, 207) of    the racks (202),-   (c) conveying the heated fluid coolant leaving the heat exchanging    means (206, 207) of the racks (202) (return flow) to the source    providing coldness, said source being located outside the space    housing the multiplicity of racks, to remove the heat from the    heated fluid coolant to a temperature of 1K to 5K, preferably 1K to    3K, more preferred 1K to 2K, below the temperature of the fluid    coolant return flow and returning the fluid coolant to the at least    one first cooling circuit.

The present invention provides for a method for operating a data centre,avoiding the necessity of guiding the cooling air across all racks tocreate cold aisle within the data centre. The only active means aretypically fans contained within the aforementioned IT equipment, whichcreate an air flow (205) in the individual rack towards the heatexchanging means of the respective rack. These active means, such asbuilt-in fans in the IT equipment, typically do not exceed 10% of theelectrical power of the IT equipment installed and operating.

While still using the present invention one may use non-substantiveactive means which do not contribute to the air flow (205) in the rack,e.g. by installing fans other than those contained within theaforementioned IT equipment. Such non-substantive contribution of suchadditional non-substantive active means provide at most 10% of the airflow (205) generated by the active means contained within theaforementioned IT equipment.

The present invention provides for a method for operating a data centrecontaining racks housing IT equipment. Such IT equipment includes allelectronic equipment used in connection with IT equipment, whichgenerates heat during operation.

The present invention provides for a method in which at least onecooling circuit is operated supplying a fluid coolant into the datacentre for cooling. In the present invention, the temperature of thefluid coolant entering the data centre and the temperature of the fluidcoolant entering the heat exchanging means (206, 207) is almost equal,which means that the temperature of the fluid coolant entering the datacentre is at most 0.2K below the temperature of the fluid coolantentering the heat exchanging means (206, 207).

In a preferred embodiment the present invention provides for a methodfor operating a data centre in which the power density of the ITequipment in the racks being at least 5 kW (electrical) per rack, morepreferred at least 8 kW (electrical) per rack, most preferred at least10 kW (electrical) per rack. The upper limit for the power density perrack is mostly limited on the space available inside the rack. Thus theupper limit is not limited per se and typically can reach up to 1 kW or1.5 kW per height unit in the rack. For a typical rack the power densityper rack amounts up to 42 kW (electrical) per 42 height unit rack.

The present method avoids the necessity of false floors used in thatcontext, too. In addition, the invention aims at optimizing energyrequirements and costs plus at arranging the computer racks more denselyin order to minimize the required length of the network cables and toimprove the system's communication capabilities.

The present method for operating a data centre allows the data centre tohave a compact structure comprising larger, scalable capacities and anincreased volume density. The present method for operating a data centrecan be used for two dimensional arranged data centres, where the racksare located on one level, or for three dimensional arranged datacentres, where the racks are located on more than one level within thedata centre.

The benefit of the present method for operating a data centre increaseswith the power density of the IT equipment installed within the racks.Such increased packing or storage density for IT equipment, such ascomputer hardware, which provides a heat dissipation, which can evenexceed a volumetric heat dissipation rate of 1 kW per m³ and more,preferably 1.5 kW per m³ and more, more preferably 2 kW per m³ and more,more preferably 3 kW per m³ and more, which cannot be achieved using theconventional air cooling systems which are the state of the art systemnowadays. The aforementioned volumetric heat dissipation rate is basedon a data centre having 2.5 m ceiling height and the net area used inthe data centre. The net area of the data centre is the area, which isoccupied by the racks housing the IT equipment, excluding any additionalspace for technical building infrastructure, such as transformers, powergenerators, battery rooms, fire extinguishing systems, storage area andthe like. In the preferred embodiment of the invention a rack is 120 cmdeep and 70 cm wide. The racks are mounted with a distance of 120 cmbetween rack rows. Therefore in the preferred embodiment of theinvention a rack consumes 1.7 m² of floor space and 4.2 m³ of the netdata centre area. Closer configurations, for instance with 60 cm wideracks and smaller distances are conceivable.

Thus the net area of the data centre used in connection with the instantinvention is the surface used to house the IT-equipment racks. It istotal surface of the data center minus the surface used for technicalinfrastructure (power supply, cooling, UPS, batteries, generators, firemanagement and other), for the access infrastructure (non-secured andsecured zones), preparation and storage surface for IT-equipment as wellas the IT-control rooms and other surface needed for the management ofthe data center.

For practical reasons the volumetric heat dissipation rate inconventional air cooling system, typically, does not exceed 6 kW perRack, which corresponds to about 2.5 to 3 kW/m² and about 0.7 to 0.9kW/m³ using the aforementioned assumptions.

All power densities per rack and other units derived therefrom refer tothe electrical power of the IT equipment installed and operating in therespective rack.

As explained above, the benefit of the present method for operating adata centre increases with the power density of the IT equipmentinstalled and operating within the racks. In particular, for data centrehaving racks with installed and operating IT equipment creating avolumetric heat dissipation rate which corresponds to least about 5kW/m², preferably to least about 10 kW/m², most preferred to least about20 kW/m², using the aforementioned net area of the data centres/datacentres room housing the racks, an extremely efficient cooling isprovided.

The present method for operating a data centre implements open rackswith passive heat exchangers, said heat exchanging means being anelement of the racks or an element attached to the racks, which arebuilt such, that most of the heated air, in the best mode the entireheated air of the IT equipment installed inside the rack is cooled backto the set room temperature. Preferably the heat exchangers are locatedon the back side of the rack. The actual position of the heat exchangersis determined by the direction of the air flow (205) generated by theactive means of the IT equipment. In a preferred embodiment of theinvention, the angle of incidence of the air flow generated towards thesurface of the heat exchanger is at most 75°, more preferred at most60°, more preferred at most 45°, more preferred at most 20°, mostpreferred between 0° and 20°.

The design of the passive heat exchanger being an element of the racksor an element attached to the racks, preferably being located at theback side, of the racks is also important because if they produce a veryhigh back pressure towards the natural airflow the overall coolingefficiency is reduced. Avoiding such back pressure inside the rack hasmanifold advantages. First heterogeneous equipment can be mounted insidethe rack because the low back pressure cannot have a negative effect onthe airflow of other IT equipment. For instance a high power server,mounted below a low power server will not push it's hot exhaust air backinto the low power server, provided there is little back pressure insidethe rack. A second advantage is that there are little requirementstowards the sealing of the cable feeds through the rack. Normal cut-outsor cable openings require self-sealing inserts, such as e.g. KoldLok®sealings. The use of such self-sealing inserts in the instant inventionis possible but not mandatory. Due to the avoidance of state of the artair-cooling and that guided air flows in the data centre are notrequired; the potential leakage rate of hot air is very limited in theinstant invention.

The room temperature of the space housing the multiplicity of rackscorresponds to the cold air exhaust of the passive heat exchangers beingan element of the racks or an element attached to the racks and istherefore connected to the fluid coolant temperature. Preferably, theroom temperature of the space housing the multiplicity of racks is about+2K, more preferably +1K, more preferably +0.5K, most preferred aboutthe same, of the temperature of the return flow of the fluid coolant ofthe first cooling circuit. The instant method providing highly efficientcooling of the racks allows for higher room temperatures as there are norisks of heat loops anywhere in the data centre. The only area of hotair is inside the racks.

The back cooling can be realised via the aforementioned source ofcoldness, including but not limited to, external cold water sources,such as ground or surface water, evaporation cooling which operatesbased on the evaporation principle, including evaporation cooling towerswith or without open cooling towers, hybrid coolers, dry coolers and thelike, and any other state of the art cooling techniques, includingcompression chillers.

The highest cooling and cost efficiency is achieved by usage of counterflow, indirect draft, wet cooling towers. The cooling principle of suchcooling towers uses the evaporation heat of water by evaporating water.For instance to cool a 1 MW data centre about up to 1.7 m³ of fluidcoolant, such as water, are required for evaporation per hour. Thecooling tower is entirely passive except a fan, which is typicallyoperated only if the outside air temperature exceeds 15° C. The lowesttemperature achievable, using open wet coolers corresponds to the wetbulb temperature. It is measured psychometrically by covering athermometer with wet cloth. The usage of evaporation coolers ensuresthat the coldest water supply temperature is above the dew point.Therefore there is no risk of condensation anywhere inside the datacentre. The water supplies do not have to be insulated.

The operating method of the preferred embodiment of this invention useswater as cold fluid coolant, in which the fluid coolant entering thedata centre for cooling via the at least one cooling circuit hastemperature almost equal to the temperature entering the heat exchangingmeans (206, 207). In this context, almost equal means that thetemperature of the fluid coolant entering the data centre is at most0.2K below the temperature of the fluid coolant entering the heatexchanging means (206, 207).

In a preferred embodiment, the instant method operates with atemperature of the return flow of the fluid coolant of the first coolingcircuit being dependent on the particular power density installed andoperating in the racks. For power densities of up to 10 kW (electrical)per rack, the temperature of the return flow of the fluid coolant of thefirst cooling circuit being at most 3K, preferably at most 2K, mostpreferred at most 1K, above the temperature supplied by the source ofcoldness entering the data centre and for power densities of at least 10kW (electrical) per rack, the return flow of the fluid coolant of thefirst cooling circuit being at most 4K, preferably at most 3K, above thetemperature supplied by the source of coldness.

The aforementioned temperature difference between the return flow of thefluid coolant of the first cooling circuit and the fluid coolant inputflow can also be higher for reduced fluid coolant flow rates. Therebythe power demand by the required pumps operating the cooling circuit isreduced during colder seasons or periods of colder outside temperatures,typically at outside temperatures below 17° C., when the back coolingsystem/source of coldness produces/provides sufficient lowtemperature/cold fluid coolant at no extra costs.

Typically the racks used in the instant method are common 19″ rackenclosures. In a preferred embodiment, the racks are tall racks whichare particularly space-saving. The racks are placed on the floor of thebuilding and not necessarily on false floor systems. Pipes and/or cabletrays are mounted above the racks. In case of an existing false floorfor the retrofit of an existing data centre such false floor can beequally used to conduct the pipes. The heat exchanger doors can beconnected to the cooling circuit from below and above. In a furtherpreferred embodiment such as the data centre being a mobile data centre,the racks are connected to the surrounding enclosure via shock-absorbingmeans, thus protecting the racks and any associated/connected means,like heat exchanging means and cooling pipes, against vibration andshocks during transportation and assembly.

The term “open” in connection with the present racks means that thefront of the racks is open and allows the IT equipment inside the rackto intake room air without flow resistance. It is also possible to havean open front door, e.g. a lattice door, which allows air to flowthrough without substantial flow resistance. Such lattice door is thepreferred embodiment as it allows the measurement of the temperature ofthe air-intake. In this preferred embodiment, two measurements arecarried out, typically one at one third height of the lattice door, andthe second at about two thirds height of the lattice door. The open rackconcept operated in the instant method allows intake of room air andexhausting of such air taking up the heat generated by the IT equipment.In a preferred embodiment, the air entering the open rack and the airexiting the IT equipment towards the heat exchanging means (206, 207)are separated by decoupling means inside the rack, separating the airexiting the IT equipment towards the heat exchanging means (206, 207)from the air entering the open rack to ensure that no heated air issoaked into the IT equipment.

Another advantage of the rack-based heat exchanging means is that theracks themselves do not have to be kept closed and that the air flowinto and out of the racks does no longer have to be controlled. As afurther benefit, inside the data centre, there are no additional airconditioners required, as the cooling function may be completely takenover by the heat exchanging units of the racks.

The racks used in the present invention do not have any other activemeans, in particular fans, for creating an air flow in the rack towardsthe heat exchanging means being an element of the racks or an elementattached to the racks. Only the IT equipment located in the respectiveracks having active means, preferably fans, for cooling parts of the ITequipment, preferably the CPU and/or GPU and/or a storage hardware, andonly said active means cooling parts of the IT equipment creating an airflow in the rack towards the heat exchanging means being an element ofthe racks or an element attached to the racks.

The instant method for operating a data centre does not require datacentre having false floor and cold aisles arrangements or design.

Most preferred are passive heat exchangers having a depth of about 50 to120 mm which can cause only a very low air back pressure. Therefore hotair leaving the IT equipment in the racks can pass the heat exchangerall by itself.

As already mentioned, the power density in modern computers has reached1 kW and even more per height unit installed in a rack. The activecooling means of the IT equipment installed in a rack, such as the fansfor cooling parts of the IT equipment, preferably the CPU and/or GPUand/or a storage hardware, create appropriate air flow rates to removethe entire heat from the IT equipment. The air flow rate depends on thetemperature difference ΔT between the air entering the rack and the airleaving the IT equipment. Typical temperature differences are ΔT=5 to 30K. This temperature difference requires an air volume current of 100 to600 m³/(h*kW), which corresponds to at least 0.5 m/s, preferably of atleast 0.8 m/s, in particular of at least 1.1 m/s.

State of the art IT equipment is designed to operate at a temperaturedifference between cold and hot air around 10 K. Therefore, the air flowrate inside a 42 height unit 19-inch rack is a linear function of thepower generated by the electronic equipment and the average airtemperature difference generated by the equipment. Hence, operating withthe 10 K difference and having IT equipment installed corresponding to20 kW electrical power, an air volumetric current of 6000 m3/h whichcorresponds to an air flow rate of 2.1 m/s for such 42 height unit19-inch rack is suitable. Such air flow rate in the instant method issolely created by the active cooling means of the IT equipment perheight unit installed in a rack, such as the fans for cooling parts ofthe IT equipment, preferably the CPU and/or GPU and/or a storagehardware.

The instant method for operating a data centre allows the transfer ofthe heat generated by the IT equipment installed inside the rack to thefluid coolant without any additional active elements.

In case the racks are not fully equipped with IT equipment, it isbeneficial to close large open slots, e.g. being greater than 3 heightunits, inside the rack in order to avoid hot air leaving the racktowards its front side. Small openings for cabling do not present aproblem due to the low pressure inside the rack.

The instant method for operating a data centre preferably allowsefficient cooling of a data centre in which the power density of the ITequipment in the racks being at least 5 kW (electrical) per rack, morepreferred at least 8 kW (electrical) per rack, most preferred at least10 kW (electrical) per rack. The upper limit for the power density perrack is mostly limited on the storage space available. Thus the upperlimit reaches typically 1 kW per height unit in the rack, thus typicallyamounting up to 42 kW (electrical) per rack.

The racks used in the instant invention typically have dimensions of 1.2m×0.7 m×2 m and are preferably arranged front to back for highestefficiency and back to back for highest redundancy.

While most IT equipment, such as servers, implement a front-to-backairflow there are exceptions to this rule. For instance Cisco Nexusswitch series receive cold air at the front and the right side of thechassis while hot air is exhausted at the left and the back side of thesystem. These switches do require 1 m wide racks also. In the preferredembodiment of this invention such airflow requirements are accommodatedby use of 1 m wide racks, which seal the left front and right back ofthe rack. Similar configurations are conceivable for IT equipment usingtheir chassis sides for air intake. The side openings of the racks donot have to cover the full height of the rack. Special switchcompartments are conceivable.

Also horizontal airflow separations at the back of the rack areconceivable, for instance in order to allow very specific determinationof sources of potential smoke and for selectively switching off theappropriate servers.

Many passive sheet metal air guides are conceivable in the preferredembodiment of the invention in order to guide cold or hot air and topotentially separate regions inside the rack. Such air guides areentirely passive and do not adversely affect the cooling efficiency ofthe system. It should be noted that such air guides are generally notrequired in the preferred embodiment of the invention and are merelyused to fit existing devices into the racks.

The present method for operating a data centre implements open rackswith passive heat exchangers being an element of the racks or an elementattached to the racks, preferably as back doors, which are built such,that most of the heated air, in the best mode the entire heated air ofthe IT equipment installed inside the rack is cooled back to the setroom temperature.

The individual passive heat exchanger being an element of the racks oran element attached to the racks, and preferably is located at the backof the individual rack and capable of transferring the entire heatgenerated by the IT equipment installed and operating within the rack tothe fluid coolant.

According to a preferred embodiment of the invention, the capacity ofthe heat exchangers is given by the nature of the fluid coolant, thecoolant input flow and the temperature difference of the coolant inputflow and coolant output flow. In the instant method, the coolingcapacity of the sum of all heat exchanging means installed correspondsto the heat generated by the IT equipment installed and operating in thedata centre. Thus, the instant invention ensures that no or nosubstantial amount of heat generated by the IT equipment is released tothe space housing the multiplicity of racks, typically referred to asthe data centre.

The instant invention allows for operating a data centre in which theair entering the racks, typically from the front side, and the airleaving the racks, typically at the back side through the heatexchanging means, have the same or essentially the same temperature andsubstantially all the heat generated is removed by the heat exchangerand the fluid coolant. Preferably, the temperature of the air enteringthe racks and the temperature of the air leaving the racks, typically atthe back side through the heat exchanging means, differ by less than+2K, more preferably +1 K, more preferably +0.5K, most preferred isabout the same. Thus no heat or no substantive heat is released to thespace/building housing the racks of the data centre.

As a result, the instant method providing highly efficient cooling ofthe racks allows for higher room temperatures as there are no risks ofheat loops anywhere in the data centre. The only area of hot air isinside the racks.

The instant invention allows that the heat exchanging means directlyreceive the hot air generated by the IT equipment inside the rack andtransform this hot air back down to a desired room temperature by simplyconveying the heat to the fluid coolant conveying piping. In this way,any routing of hot air or creating any air flows inside the data centrecan be avoided. By allowing this, the distance over which hot or heatedair travels can be reduced to a minimum. It is only required totransport the heated air inside the rack, in particular from the ITequipment to the heat exchanging means. In this way, anydifficult-to-control turbulent air flow can be prevented. In addition,the instant invention does not require the high throughput flow of coldair and the problems relates with any condensation of moisture beingpresent in such air. Hence, the use of any air dehumidifiers becomessuperfluous.

According to another preferred embodiment of the invention, the heatexchanging means do not comprise any active means, such as fans, forguiding the heat/hot air from the IT equipment to the surface of theheat exchanging means or through the heat exchanging means. Therelatively low and laminar stream of air obtained from the CPU and/orGPU cooling fans inside the particular rack allow to avoid additionalfans and to avoid any additional fan power consumption.

The present method for operating a data centre uses passive heatexchangers having a low air backpressure. The air backpressure generatedby the heat exchanger depends on the air flow rate. The heat exchangersused in connection with the instant method preferably have an airbackpressure of maximum 10 Pa for air flow rate corresponding of up to0.5 m/s, more preferred of maximum 16 Pa for air flow rate correspondingof up to 0.8 m/s, most preferred of maximum 20 Pa for air flow ratecorresponding of up to 1.1 m/s.

The aforementioned air flows and air back pressure work well with the ITequipment installed in the racks, which typically operate within thetemperature difference between cold and hot air being around 10K.

The instant method uses fluid coolant system. One major concern in datacentres it the potential of leaks, in particular for water being used asfluid coolant.

The risk of water spills and the amount of damage caused by spillscorresponds to the pressure of the water system. Therefore, a furtheraspect of the instant method is to use heat exchangers having a lowpressure drop across the heat exchanger.

The present method for operating a data centre uses passive heatexchangers having a low pressure drop across the heat exchanger.

The pressure drop across the heat exchanger depends on the volumetricfluid flow of the fluid coolant. Therefore, in the instant invention,the passive heat exchangers situated at the backside of the racksprovide preferably a pressure drop below 22 kPa for a volume current of3 m³/h for water, preferably below 54 kPa for 5 m³/h for water, mostpreferred below 200 kPa for 10 m³/h for water.

Operating at a pumping rate below 5 m³/h for water, the instant methodcan be accomplished below atmospheric pressure of the fluid coolantbeing water.

The present method for operating a data centre requires controlling thefluid coolant flow within the first cooling circuit (205) which isadapted to supply the heat exchanging means (206, 207) of the racks(202) to maintain the temperature of fluid coolant entering the heatexchanging means (206, 207) of the racks (202) (input flow) having atemperature of 1K to 5K, preferably 1K to 3K, most preferred 1K to 2K,below the temperature of the fluid coolant return flow exiting the heatexchanging means (206, 207) of the racks (202). Thus, the flow rate forthe fluid coolant, such as water, is preferably from 0.9 m³ per hour andper kW installed and operating for a difference of 1K and to 0.17 m³ perhour and per kW installed and operating for a difference of 5K.

One remaining concern was the potential power increase caused by theservers' cooling fans due to the back pressure of the heat exchanger.This was tested by opening and closing the back door of the rack anddetermining the total power consumption of the computers inside therack. Both the total power consumption of all servers in a rack and thesupply current to one sample fan were measured.

There was no significant difference in power consumption measured whenopening the back door, primarily due to the low back pressure.

Preferably, each rack implements autonomous power distribution units,supplying power to all electric components inside the rack andmonitoring the power consumption and electric properties, in particularfor high power densities, e.g. used in scientific applications. Thisfunctionality is provided by an embedded micro controller. It measuresin addition air input and output and cooling water temperatures. Furthereach rack implements an independent smoke detector. In case of a smokealarm or overheating the servers are configured to automatically shutdown. After exceeding configured thresholds, the PDU will ultimately cutthe power. Such safety measures are important per rack because of thehigh power density and corresponding fast temperature rise in case of acooling failure.

The heat exchanging means of the racks are connected to a coolingcircuit which supplies fluid coolant, preferably liquid coolant, to eachof the heat exchanging means through a piping system.

In a preferred embodiment of the invention, the cooling circuitcomprises a piping system to remove the coolant. Usage of a liquidcoolant such as water and other suitable cooling fluids, particularlywith larger thermal capacities than air, is advantageous due to numerousreasons. At first, the total heat quantity that may be transferred andtransported is, compared to gaseous coolants, much larger. Secondly, itis possible to control and monitor the flow and the transmission of thecoolant more easily, compared to a turbulent and laminar flow of agaseous coolant.

In another embodiment of the invention, the pressure of the liquidcoolant can be set up to below 2bar, so that in case of a leakageminimal fluid ejection of the liquid occurs and the leakage liquid flowsalong the cooling circuit. In such embodiment the cooling circuit mayhave a hollow/sink to collect any such leakage liquid preventing thatany such leakage liquid comes into contact with the computer hardware.The piping is arranged behind the rack's back door, which presents aprotection of the IT equipment against water spills due to the finegranular heat exchanger structure. In both cases any leakage in thepiping system can be detected by monitoring the pressure in the pipingsystem and set an alarm thus allowing to take appropriate measuresagainst such leakage, such as for instance the stopping of the pumps, inorder to reduce the pressure further and to stop the continued watersupply to the leak.

Further no insulation of the piping system is required as the roomtemperature corresponds to the cold water return temperature, which issignificant higher than the dew point.

The data centre has at least one source providing coldness beingconnected either directly or indirectly to the first cooling circuit asmentioned before.

Most typically, the source providing coldness is at least one coolingtower operating with counter flow, indirect draft, wet cooling tower, inwhich water is sprayed from the top of a column and cooled byevaporation of some of the water and thereby collected downwards. Inorder to avoid contamination of the first cooling circuit, the sourceproviding coldness can be decoupled from the source providing coldnessby a second cooling circuit. Such decoupling is typically achieved byredundant heat exchangers which transfer heat from the first coolingcircuit to the second cooling circuit.

By way of this implementation any contamination of the second coolingcircuit being directly connected to the source of coldness, which may becontaminated by air particles, such as pollen, is separated from thefirst cooling circuit going inside the data centre. The necessary pumpsfor pumping the fluid coolant can be placed inside the data centre oroutside the data centre.

Depending on the environmental climate, in some geographical areascommon water chillers cause problems, e.g. during cold/freeze periods.In such cases it is preferred to use so-called hybrid cooling towersinstead. Most typically such hybrid coolers are plate heat exchangerthrough which the heated coolant is flowing through and cooled by theenvironmental air. One example for a hybrid cooler is shown in U.S. Pat.No. 7,864,530. To increase the cooling capacity in summer, it ispossible to spray water to the surface of the plate heat exchanger anduse the evaporation cooling of such water. Since these hybrid coolingtowers include a heat exchanger no further heat exchangers are required.However, the cooling water may require additives, such as glycol inorder to prevent it from freezing.

Further, the source providing coldness has means for conveying theliquid coolant to the cooling circuit entrance. Such means typically arepipes, preferably being flexible, made of different materials, such assteel, stainless steel and/or synthetic organic polymer materials.

In another embodiment of the instant invention, the data centre situatedin a unit such as a container or the data centre is built using racksbeing pre-installed in support frames, which preferably are standardsize frames. This allows for pre-installation/pre-assembly when buildingdata centres or for mobile data centres. Preferably such standard sizeframes, units or container having the typical standard size of a commonISO container which can be transported, loaded and unloaded, stacked andtransported efficiently over long distances by ship, rail, trucks,semi-trailer trucks or planes. Most preferred are 20-ft (6.1 m), 40-ft(12.2 m), 45-ft (13.7 m), 48-ft (14.6 m), and 53-ft (16.2 m) longunits/containers. The width typically is 10 ft (3.0 m) to 8 ft (2.4 m)and the height typically is 9 ft 6 in (2.9 m).

The present method for operating a data centre provides a fluid coolantfrom the source providing coldness to the heat exchanging means (206,207) of the racks (202) within the first cooling circuit, said fluidcoolant input flow having a temperature of 1K to 5K, preferably 1K to3K, most preferred 1K to 2K, below the temperature of the fluid coolantreturn flow exiting the heat exchanging means (206, 207) of the racks(202).

Preferably, the temperature of the fluid coolant entering the heatexchanging means is adjusted to 0.1 to 0.5K per kW installed andoperating per Rack not exceeding 10 kW per Rack, below the temperatureof the fluid coolant return flow exiting the heat exchanging means (206,207) of the racks (202).

Preferably, the temperature of the fluid coolant entering the heatexchanging means is adjusted to 0.1 to 0.2K per kW installed andoperating per Rack amounting between 10 kW and 25 kW per Rack, below thetemperature of the fluid coolant return flow exiting the heat exchangingmeans (206, 207) of the racks (202).

Preferably, the temperature of the fluid coolant entering the heatexchanging means is adjusted to 0.1 to 0.125K per kW installed andoperating per Rack amounting to above 25 kW per Rack, below thetemperature of the fluid coolant return flow exiting the heat exchangingmeans (206, 207) of the racks (202).

The present method for operating a data centre allows for efficientcooling of a data centres. For example, the coldest temperatureachievable with state of the art back cooling technology usingevaporation cooling is the wet bulb temperature, which in Europe hardlyreaches 22° C. The appropriate wet bulb temperatures are available atthe local weather services. Typically the fluid coolant, in particularthe cold water, supply is about 2 K warmer than the wet bulbtemperature, which is the theoretical limit. In the preferred embodimentof the invention the heat exchanger adds another 2 K between thesecondary and first circuit. However, it should be noted that thistemperature difference is only a function of the size of the heatexchanger and can be cost optimised. For example, a temperaturedifference of +1K in the first cooling circuit (difference between heatexchanger outlet and inlet), which would correspond for example to 9m³/h water as fluid coolant and 10 kW electrical power of the ITequipment installed and operating inside the racks, the lowest fluidcoolant, in particular cold water, return of the cooling system is 5Kabove the wet bulb temperature. Allowing for another +1K difference tothe room temperature due to radiation of the warm racks, warm air leaksthe room temperature is 6K warmer than the wet bulb temperature. Thislimit can be even reduced by increasing the pumping rate, but at thecost of higher power requirement of the pumps. However, taking intoaccount that for instance in Germany the wet bulb temperature exceeded20° C. during the years 2007 through 2011 for about 140 hours onaverage. Therefore only a small fraction of the time the pumps wouldhave to operate on high pumping rate and therefore will only generate asmall addition to the overall power budget. During cold outsidetemperatures the cooling system is throttled in order to keep the roomtemperature above 20° C.

It should be noted that basically all commercial computer systems andnetwork components are rated to operate up to 35° C. at nearly constantwalk according to ASHRAE TC 9.9 (2011) and ETSI EN 300 019-1-3; V2.3.2.(2009-07). Many vendors have announced to even increase this figuretowards higher temperatures because all cooling systems improve inefficiency with increased room temperatures.

If the fluid coolant, in particular cold water, return reaches 30° C. itcan be used to heat buildings if they implement floor or wall heatingwithout any heat pumps. The only additional power required is the pumpto move the water through the heating manifolds inside the building andto potentially push it up towards higher floors. In summer the floorheating can be connected to the cold water supply and therefore be usedfor very efficient cooling of the building, however at additionalcooling requirements for the cooling towers.

Most typically, most or even all racks are individually connected to thecooling circuit, which provides an efficient instrument for removing anddischarging the heat from the computer hardware.

Coupling each rack to be cooled to the cooling circuit individually withthe cooling circuit in connection with the rack-specific heat exchangerssuitable to remove the entire heat generated by the computer hardware,provides the additional advantage that it is possible to control andmonitor the cooling power and heat exchange individually and separatelyfor each individual rack within the structure of the data centre.Cooling the hot air exclusively within the rack makes it possible toinstall any rack package densities without requiring air flow design,such as cold aisles or hot aisles.

The present instant invention allows using a so-called open rackarchitecture ensuring the racks do not need to be hermetically sealedanymore. Such open rack structure further allows easier access to the ITequipment, in particular the computer hardware, inside the rack, in caseof any problems or maintenance needed. Due to the low pressure of theair flow at the rear side of the IT equipment normal openings forcabling can be easily closed.

Another preferred aspect of the present invention is that at least someor all of the racks comprise control means. In this way, the entiresystem may adaptively, locally react on local system failures and mayautomatically initiate respective provisions in order to compensate thefailure.

According to another embodiment, the control means further comprisetemperature sensors, leak detectors for the piping and/or the smokedetectors, whereby said detectors are coupled to an emergency alarmsystem, which is adapted to selectively switch off the hardware, rackand/or the relevant portion of the cooling pipe unit.

The emergency system may be designed and arranged in any of said racksindividually and separated from an emergency system of neighboring oradjacent racks. Smoke and leakage detectors may be installed separatelyand independently from each other in order to individually switch offburning or smoking IT equipment and to be able to maintain all otheroperations of the data centre. Alternatively, it may also be imaginableto use a combination of individual detectors and/or to use amulti-functional detector.

According to a further embodiment, the racks further comprise powerscheduling means, that are adapted to keep an overall rush-in electriccurrent below a predefined threshold. This embodiment is adapted toprevent, that the entire data centre draws an amount of energy whichcannot be provided by an external power supply. Therefore, the powerscheduling means are adapted to regulate, that each rack or a pair/groupof racks draws power from an electric current- or voltage supplyaccording to a given time sheet.

For instance, a first rack may power-up after a given time-delaycompared to any other rack of the data centre. In this way, peak-powerconsumption of the entire data centre can be kept below a predefinedthreshold, thus ensuring, that the external power supply does not breakdown. The power scheduling means may either be implemented as a specificalgorithm assigning a predefined individual, hence different, time-delayto any of the racks of the data centre building.

Alternatively, it is also conceivable, that a power switch-on of thevarious racks is controlled by means of a centralized architecture.However, also an interconnected emergency system is in the scope of thepresent invention, whereby a multiplicity of leak- and/or smokedetectors are electrically coupled to a central emergency system, whichmay automatically initiate respective provisions in order to counteracta system failure.

According to another preferred embodiment, the data centre furthercomprises at least one further cooling circuit, for example a redundantfirst cooling circuit, comprising the same principal structure than thefirst cooling circuit which takes over the duty of the first coolingstructure in case of any leakage or other problem. Preferably, thecooling circuit, including the first cooling circuit, has at least twofluid coolant intakes which allows operation also in case of anyleakage, partial shut-down.

According to yet another preferred embodiment, all pumps in the datacenter have a redundant backup pump, which can be activated in case ofthe primary pump failing. Proper shut-off valves allow the replacementof a broken pump while the system is operating.

The instant method allows operating the data centre at relatively highambient temperatures, e.g. up to 30° C.

The preferred embodiment of the invention implements an additionalredundancy if the racks are mounted back-back. In that case the cold airof two rack rows is mixed in the aisle between the racks. The two rackrows can easily be made independent by use of independent pipes andpumps. In case of an entire rack row failing due to a catastrophic leakor a failure of all redundant pumps the air leaving the racks connectedto the failing cooling system will slowly rise until the servers exitair temperature is reached, which is typically 10K higher than theambient temperature. For a rack with 10 kW power consumption thetemperature rise is about 3K per hour. The warm air leaving the rack rowwith the failing cooling system is mixed with the air of the oppositerack row. Therefore the air temperature inside the aisle is on averageonly 5K warmer than the ambient temperature. This temperature rise canbe compensated by lowering the cold water supply to the rack row withthe working cooling system.

The power utility efficiency (PUE) used in connection with the instantinvention is defined in “Data Center Efficiency Metrics—PUETM, PartialPUE, ERE, DCcE” (2011) by Dan Azevedo, Jud Cooley, Michael Patterson andMark Blackburn published on www.thegreengrid.org. The by far largestcontribution to the power overhead of a data centre is the cooling.Additional contributions are electric transformations and distributions,backup power generation, such as battery backup systems, airconditioning and the like. The presented invention allows reducing thecooling overhead to a minimum. The instant method allows operating thedata centre at a power utility efficiency (PUE) of at most 1.3,preferably at most 1.2, more preferred at most 1.15, in particular atmost 1.1

In the following, the invention will be described in detail by makingreference to the drawings in which:

FIG. 1 schematically illustrates a data centre operating according tothe instant method

FIG. 2 schematically illustrates a heat exchanging unit of a datacentre, according to an embodiment.

In the illustrated embodiment of FIG. 1, any of the racks (202)comprises a separate heat exchanging unit (206), which is equipped witha heat exchanger (207). The active means, such as the CPU cooling fan,of the IT equipment (200) facilitates an air flow (205) inside the rack(202) towards the heat exchanging unit (206). The heat exchanging units(206) are all coupled to a piping (203/204) conveying a liquid coolant,e.g. water, to any of the racks (202).

The coolant supplied by means of a piping (203/204) is beneficial inthat the various racks (202) are entirely passive and no longer have tobe designed as closed racks. Moreover, heat dissipation outside thevarious racks (202) can be effectively reduced to a minimum or evencompletely avoided. Hence, it is no longer necessary to control a globalair stream inside the building structure. In this way generation of hotspots which might be due to some uncontrolled hot air flow outside theracks (202) can be effectively eliminated.

Additionally, the airflow throughout the data centre building structuredoes no longer have to be actively controlled, since the ambienttemperature around the racks (202) is kept on a relatively cold levelcompared to the temperature inside the racks (202).

In order to implement failure tolerance on the cooling infrastructure,the racks (202) can be operated in an even/odd fashion, where everysecond rack is coupled to the same piping, namely either the first orsecond redundant first cooling circuit. In this way, two redundant firstcooling circuits can be maintained providing a residual coolingcapacity.

In case of a failure, for instance due to a leak in the piping(203/204), a particular rack can be selectively decoupled from thepiping system (203/204).

Since there is no requirement to guide any air throughout the datacentre structure, such as the space housing the multiplicity of racks,the IT equipment (200) containing racks (202) can be placed in anyarbitrary arrangement. A data centre within the meaning of the instantinvention contains more than one rack (202).

Rising the ambient temperature in the data centre therefore rises thefluid coolant, in particular cooling water, temperature, which directlyincreases the cooling efficiency of the heated fluid coolant, inparticular the heated cooling water.

REFERENCE LIST OF REFERENCE NUMERALS

200 IT equipment (having a power density 224) 201 grid floor 202 rack203/204 piping system for first cooling circuit 205 air flow inside therack, solely created by active means contained in the IT equipment 206heat exchanging unit 207 heat exchanger 208 height units for ITequipment 210 IT equipment fan 212 input air entering front side ofracks (having room temperature 222) 214 fluid coolant flowing throughheat exchanging units 214A input flow of fluid coolant (having an inputcoolant temperature 218A and volumetric fluid flow 226) 214B output flowof fluid coolant (having an output coolant temperature 218B andvolumetric fluid flow 226) 216 air back pressure of heat exchanging unit220 cold air exhaust temperature of air exiting heat exchanging unit 230coolant source 232 wet bulb temperature (in proximity to the coolantsource) 234 fluid pressure drop across a heat exchanging unit

Example 1

A data centre, hosting a high performance computer consuming 500 kW ofpower and being installed in 34 racks each 19-inches and having 42height units. The racks are 1.2 m deep and 70 cm wide. The rack floorspace requires less than 100 m² net area.

The cooling infrastructure mainly consists of two cooling circuits,connected by a heat exchanger. The first cooling circuit transfers theheat generated in the data centre's 19-inch racks to a heat exchanger,which is cooled back by the secondary circuit. The secondary coolingcircuit uses two 313 kW counter flow, indirect draft, wet coolingtowers, where the makeup water is taken from a neighbouring river. Theentire cooling infrastructure is mounted inside a 20 ft container withtwo cooling towers mounted on the roof. Said towers can be maintainedand cleaned one at a time while the cooling system remains active but atreduced power. It should be noted that this scheme requires a minimum of50 kW computer power in order to avoid freezing of the cooling systemsduring winter. An emergency water draining infrastructure is installed.

The entire cooling system implements three electrical consumers: thesecondary pump (6 kW), the first cooling circuit pump (28 kW) and onefan in every cooling tower (4.5 kW each). While the fan power can bethrottled, as the fans are not required at outside temperatures below15° C., the two water pumps are configured to run at a constant, fixedvolume current of 150 m³/h in the secondary and 220 m³/h in the firstcooling circuit. The water flow rate in the first cooling circuit issufficient to cool up to 900 kW power, while the secondary circuitsupports up to two times 313 kW to date. An upgrade of the system to atotal power of 900 kW is possible by adding one additional cooling towerto the existing infrastructure. With the assumption of a typical 35%average utilization of the cooling tower fans and 500 kW maximum HPCpower, an average cooling overhead of 7.4% or PUE=1.074 results. In caseof the fully utilized cooling system with a power load of 900 kW, thecooling overhead would be 4.9% or PUE=1.049. Further optimizations areconceivable in particular in case of the secondary pump. In case of thisimplementation the pump has to drive the volume current over a largedistance of 120 m because the cooling container could not be placedclose to the data centre room.

Example 2

A mobile data centre container having 3 m width, 2.9 m height and 12.2 mlength is equipped with 13 19″ racks, each having IT equipment whichoperates at 35 kW. The total power of 455 kW is cooled back by a hybridcooler. The water pump requires 10 kW and the hybrid cooler requires anadditional 6 kW, which results in a power utility efficiency ofPUE=1.035.

1. Method for operating a data centre comprising: (i) a building forhousing a multiplicity of racks (202), each rack being an open rackhousing IT equipment, (ii) the racks (202) being an open rack housing ITequipment (200) (iii) the racks (202) comprise heat exchanging means(206, 207) being adapted to transfer the heat generated by the ITequipment to a fluid coolant, said heat exchanging means being anelement of the racks or an element attached to the racks, preferablybeing located at the back side or element of the racks, (iv) at leastone first cooling circuit (203/204), said cooling circuit being a closedcooling circuit, which is adapted to supply the heat exchanging means(206, 207) of the racks (202) with a fluid coolant and is furtheradapted to convey the heated coolant away from the heat exchanging means(206, 207) of the racks (202) through the reflux of the cooling circuit,(v) said first cooling circuit (203/204) being connected to a sourceproviding coldness, said source being located outside the space housingthe multiplicity of racks, (vi) the IT equipment (200) located in therespective racks (202) having active means, preferably fans, for coolingparts of the IT equipment (200), preferably the CPU and/or GPU and/or astorage hardware, said active means creating an air flow (205) in therack (202) towards the heat exchanging means (206, 207) being an elementof the racks or an element attached to the racks, preferably beinglocated at the back side or element of the racks (202), (vii) said racks(202) having no other active means, in particular fans, except for thosecontained within the aforementioned IT equipment (200), for creating anair flow (205) in the rack (202) towards the heat exchanging means (206,207) being an element of the racks or an element attached to the racks,preferably being located at the back side or element of the racks (202),(viii) said building for housing the multiplicity of racks (202)comprising no other active means, except for those contained within theaforementioned IT equipment (200), for creating an guided air flow, (ix)at least one electrical power input, (x) at least one mean fordistributing the electrical power from the power input to the individualracks, allowing redundant power supplies in every rack, comprising themeasures (a) providing a fluid coolant from the source providingcoldness to the heat exchanging means (206, 207) of the racks (202)within the first cooling circuit, said fluid coolant input flow enteringthe heat exchanging means (206, 207) having a temperature of 1K to 5K,preferably 1K to 3K, most preferred 1K to 2K, below the temperature ofthe fluid coolant return flow exiting the heat exchanging means (206,207) of the racks (202), (b) controlling the fluid coolant flow withinthe first cooling circuit (203, 204) which is adapted to supply the heatexchanging means (206, 207) of the racks (202) to maintain thetemperature of fluid coolant entering the heat exchanging means (206,207) of the racks (202) (input flow) having a temperature of 1K to 5K,preferably 1K to 3K, most preferred 1K to 2K, below the temperature ofthe fluid coolant return flow exiting the heat exchanging means (206,207) of the racks (202), (c) conveying the heated fluid coolant leavingthe heat exchanging means (206, 207) of the racks (202) (return flow) tothe source providing coldness, said source being located outside thespace housing the multiplicity of racks, to remove the heat from theheated fluid coolant to a temperature of 1K to 5K, preferably 1K to 3K,most preferred 1K to 2K, below the temperature of the fluid coolantreturn flow and returning the fluid coolant to the at least one firstcooling circuit.
 2. The method as claimed in claim 1, wherein the powerdensity of the IT equipment in the racks being at least 5 kW(electrical) per rack, more preferred at least 8 kW (electrical) perrack, most preferred at least 10 kW (electrical) per rack.
 3. The methodas claimed in claim 1, wherein the racks (202) being arranged as twodimensional arranged data centres, where the racks are located on onelevel, or as three dimensional arranged data centres, where the racks(202) are located on more than one level within the data centre.
 4. Themethod as claimed in claim 1, wherein the power density of the ITequipment (200) installed and operating within the racks (202) creates avolumetric heat dissipation rate which corresponds to least about 5kW/m², preferably to least about 10 kW/m², most preferred to least about20 kW/m².
 5. The method as claimed in claim 1, wherein the roomtemperature of the space housing the multiplicity of racks (202) isabout +2K, preferably +1K, more preferably +0.5K, most preferred aboutthe same, of the temperature of the return flow of the fluid coolant ofthe first cooling circuit.
 6. The method as claimed in claim 1, whereinthe source of coldness provides the back cooling through (i) externalcold water sources, preferably ground or surface water, (ii) evaporationcooling which operate based on the evaporation principle, includingevaporation cooling towers with or without open cooling towers, (iii)hybrid cooler or (iv) dry cooler.
 7. The method as claimed in claim 1,wherein the fluid coolant entering the data centre for cooling via theat least one cooling circuit has temperature at most 0.2K below thetemperature of the fluid coolant entering the heat exchanging means(206, 207).
 8. The method as claimed in claim 1, wherein the temperatureof the return flow of the fluid coolant of the first cooling circuitbeing at most 3K, preferably at most 2K, most preferred at most 1K,above the temperature supplied by the source of coldness entering thedata centre for total power densities of up to 10 kW (electrical} perrack or wherein the temperature of the return flow of the fluid coolantof the first cooling circuit being at most 4K, preferably at most 3K,above the temperature supplied by the source of coldness entering thedata centre for total power densities of at least 10 kW (electrical) perrack.
 9. The method as claimed in claim 1, wherein the method foroperating the data centre does not operate any additional airconditioners.
 10. The method as claimed in claim 1, wherein the methodfor operating the data centre does not have any other active means, inparticular fans, for creating an air flow (205) in the rack towards theheat exchanging means except for such active means being present in theIT equipment located in the rack.
 11. The method as claimed in claim 1,wherein the active means, in particular fans, being present in the ITequipment (200) create an air flow (205) in the rack towards the heatexchanging means which corresponds to an air volume current of 100 to600 m³/(h*kVV), which corresponds to at least 0.5 m/s, preferably of atleast 0.8 m/s, in particular of at least 1.1 m/s.
 12. The method asclaimed in claim 1, wherein the active means, in particular fans, beingpresent in the IT equipment (200) create an air flow (205) in the racktowards the heat exchanging means which create an air back pressure bythe heat exchanger corresponding to maximum 10 Pa for air flow ratecorresponding of up to 0.5 m/s, preferably maximum 16 Pa for air flowrate corresponding of up to 0.8 m/s, more preferred maximum 20 Pa forair flow rate corresponding of up to 1.1 m/s.
 13. The method as claimedin claim 1, wherein the pressure drop across the heat exchanger is setbelow 22 kPa for a volume current of 3 m³/h for fluid coolant,preferably water, preferably below 54 kPa for 5 m³/h for fluid coolant,preferably water, most preferred below 200 kPa for 10 m³/h for fluidcoolant, preferably water.
 14. The method as claimed in claim 1, whereinthe flow rate for the fluid coolant, preferably water, is set from 0.9m³ per hour and per kW installed and operating for a difference of 1Kand to 0.17 m³ per hour and per kW installed and operating for adifference of 5K.
 15. The method as claimed in claim 1, wherein thetemperature of the fluid coolant entering the heat exchanging means(206, 207) is adjusted to 0.1 to 0.5K per kW installed and operating perRack not exceeding 10 kW per Rack, below the temperature of the fluidcoolant return flow exiting the heat exchanging means (206, 207) of theracks (202) or wherein the temperature of the fluid coolant entering theheat exchanging means (206, 207) is adjusted to 0.1 to 0.2K per kWinstalled and operating per Rack amounting between 10 kW and 25 kW perRack, below the temperature of the fluid coolant return flow exiting theheat exchanging means (206, 207) of the racks (202), or wherein thetemperature of the fluid coolant entering the heat exchanging means(206, 207) is adjusted to 0.1 to 0.125K per kW installed and operatingper Rack amounting to above 25 kW per Rack, below the temperature of thefluid coolant return flow exiting the heat exchanging means (206, 207)of the racks (202).